Starting control for electric discharge devices



April 9, 1946. L. H. ZYTA 2,398,128

STARTING CONTROL FOR ELECTRIC DISCHARGE DEVICES Filed April 25, 1942 lnven'tor'z Leon H. Zgca,

His M'to'rneg.

Patented Apr. 9, 1946 I STARTING CONTROL FOR ELECTRIC DISCHARGE DEVICES Leon n. Zyta, Cleveland Heights, om, minor to General Electric Company, a corporation or New York Application April 25, 1942, Serial No. 410,505

2 Claims. (01. zoo-113.5)

This invention relates to the control of electric discharge devices, and is especially concerned with the starting of such devices. The invention is very useful in connection with fluorescent tubes or lamps of the positive column discharge type, and is hereinafter explained with particular reference to lamps of this character and their usual starting arrangements, as exemplified in U. S. Patent 1,951,112, March 13, 1934, to Wels, 01' U. S. Patent 2,2l2,427, August 20, 1940, to Peters, for instance.

Ordinary tubular fluorescent lamps have electrical starting circuits which are energized and broken to start the discharge. Sometimes this has to be done several times before the discharge actually starts. For this purpose, automatic means are commonly provided which will make and break the starting circuit indefinitely until starting is accomplished.

Through deterioration in service or as the result of accident, fluorescent lamps and other discharge devices often or eventually become incapable of starting and normal running, so that the only effect of the automatic efforts to start such a lamp is a continual flashing in it that is very annoying to those inthe area that receives the light of the flashing lamp, besides uselessh! wearing out the starter device. Usually the incapacity for starting is due to loss of electron emission from one or both electrodes of the lamp,

which may result from dissipation or other loss of activating material on which the emission depends. The objectionable flashing of such a lamp goes on indefinitely, until the power supply is shut oil, or the lamp is removed from the circuit.

The purpose of my invention is to obviate the undesirable flashing of defective lamps without interfering with repetition of the attempts to start as long as there is any reasonable promise of success. This I accomplish by rendering the starter either ineffective to close the starting circuiaor ineffective to open it. I have chosen this latter method for purposes of illustrative description herein, and have shown and explained the invention as applied to a glow-switch type of starter. However, the invention is also applicable to other types of starter switches.

Various features and advantages of the invention will become apparent from the description oi a species and form of embodiment, and from the drawing.

In the drawing, Fig. l is a diagrammatic view of a fluorescent tube or lamp with circuit connections including my invention; and Fig. 2 is a tilted or perspective view of a switch device suitable for the purposes ofmy invention.

I will first describe the portion or the circuits and apparatus shown which have heretofore been in use, and which permit the objectionable flashing or a defective lamp as described above.

Fig. 1 shows an ordinary fluorescent tube lam L of the positive column electric discharge type with a tubular envelope l0 having spaced-apart activated thermionic cathodes H, H in its ends, which may be specially heated cathodes of usual coiled filament type, and are shown connected across a power-supply circuit P'including the usual ballast ll, which also serves as a starting inductance, and the manual make-and-break switch IS. The envelope l0 may contain a lowpressure atmosphere of starting gas, such as argon at a pressure of 2 to 5 mm. of mercury, and

.also 'a vaporizable and ionizable working substance such as mercury. A supply of mercury, which may exceed the amount that-will vaporize during operation of the lamp L, is indicated by a drop l1 inside the envelope l0, and an internal coating of fluorescent material or phosphor l8 on the envelope walls is also indicated. A starting and electrode-heating circuit H is shown connected across theclrcuit P through the filamentary cathodes II, II, with a starting switch S included therein, which may be of thermal type.

A capacitor or condenser 19 of suitable capacity (e. g., 0.006 microfarad for a 40 watt fluorescent lamp) may be connected across the switch S, to minimize radio interference as well as arcing when the switch S opens and breaks the circuit H lamp L with this circuit arrangement is that when the switch I! is closed to turn on the lamp 'charge between them, or, in other words, starts the lamp.

As shown in Figs. 1 and 2, the thermal switch 8 is of glow-switch type,- comprising a glass envelope 20 containing a low-p re atmosphere of rare gas, such as argon at an absolute pressure oi. 25 mm. of mercury. The envelope 20 may include a stem 2| through which are sealed cur-,

rent leads I2, 23 that are connected to opposite sides or the circuit H, and are provided with ter- The general mode of operation in starting the minals or electrodes inside the envelope between which a glow discharge takes place when the switch I is first closed. In the switch 8 here illustrated, one of these terminals or electrodes consists of an upward extension 25 of the current lead 22 from the stem 2|, while the other consists of a thermostatic bimetal strip member 26 attached to the lead 23, as by welding, and coacting with the member 25 as both a temperature-responsive element and a contact for the switch S. The lead wires 22, 23 and the extension 25 may be of nickel. A contact piece 21, as of molybdenum, is shown welded tothe free end of the member 26, and extending at right angles to the contact member 25.

The general operation of such a switch S is that when the circuit H is energized as a result of closing the hand switch I5, a glow discharge takes place across the gap between the parts 25, 26. This discharge heats the flexible loop-like member 26 until it flexes or bends sufilciently to touch the member 25, thus closing the circuit H and shorting out and terminating the glow discharge. The thus augmented flow of current in the circuit H continues long enough to heat the filamentary cathodes H, H to an adequate electron-emissive temperature; and by the time this has been accomplished, the thermostatic member 26 cools and flexes sufliciently to disengage the member 25, open the circuit H, and start the main discharge between the electrodes H, H, as already described. After the main discharge has started, the voltage on the device S is no longer high enough to maintain any discharge across the gap between the parts 25, 26.

If, however, the main discharge does not start on the voltage kick due to the opening of the circuit H by the switch S as just described, a glow discharge again takes place between the pars 25, 26, and the switch S again closes and opens, just as before; and if this effort is not successful in starting the main discharge, it is repeated, and so on. If the main discharge cannot be started at all, the lamp L would (with the circuit arrangement and parts so far described) go on to flash indefinitely in the objectionable manner described above.

In accordance with my invention, means of control are provided for determining the condition of the circuit H as to continuity in such a way that after reasonable efforts of the starter S to start the main discharge, a condition of circuit H that prevents flashing of the lamp L is established and maintained, independent and regardless of any further action or operation of starter S. For this purpose, automatic control means may be employed whose period of operation (as fixed by design and adjustment) is long enough to include whatevernu'mber of attempts by starter S may be considered reasonably worthwhile: e. g., a period of some seven to ten seconds under favorable voltage conditions, embracing some five to ten attempts, say. The action of this automatic control need not be an arbitrary matter of fixed adjustment, however, but can be made responsive to the actual attempts of starter S to start the main discharge.

A simple control for this purpose is shown in Figs. 1 and 2 as comprising an electric heater 30 connected in series with the glow switch S. The heater 30 may consist of a heating resistance coil of fine nichrome wire, and with this may be associated a thermoinsulative heat shield or covering 3| to give increased thermal capacity, such as a section of glass tubing. However, the essen tial is a sufflcient thermal capacity of the heater 30 to delay the heating of the thermostatic loop 26 and give the action hereinafter described, and

such thermal capacity may be provided in various ways.

For connecting the heater 3!) in circuit, current leads 32, 33 are shown sealed through the stem 2| and extending up inside the envelope 20, and the heater 3!] is connected between their upper ends, substantially coaxial with the bend of the thermostatic strip 26. The lead 32 is com nected to one of the connectors 34, 34 on the base 35 of the glow switch casing 36, while the lead 33 is connected to the glow switch thermostat lead 23 inside the stem 2 l and the other glow switch lead 22 is connected to the other connector 34. The condenser I9 is shown connected be tween the connectors 34, 34, in shunt with the serially connected glow switch S and the heater 30. Externally, the connectors 34, 34 are connected to opposite sides of the starting circuit H.

In starting a good lamp L, the starter S functions in the usual way, just as if the heater 30 were absent. This is because the heater 30 is heated mainly by the relatively large current flowing during the periods when the switch S is closed, and only a little by the much smaller cur rent flow represented by the glow discharge in the starter S, and because the large thermal capacity of heater 36 (due to the shield 3|) re quires accumulation of heat from more than a mere couple of operating cycles of the starter S to raise the temperature sufliciently to influence the thermostat 26 decisively. It", then, several operating cycles of the glow switch S suflice to start the discharge in the lamp L, all current flow through the circuit H ceases, and the heater 30 cools off without having affected the action of the starter S materially.

In the case of a defective lamp, that cannot be started, the operation of the starter S and the accumulation of heat and rise of temperature in the heater 30 continue through a number of cycles of the starter S, until the heater 30 becomes hot enough to heat and operate the thermostat 25 to close the switch S and the starting circuit H independently of glow switch action of the starter. When this happens, the current flowing through the heater 30 maintains its temperature high enough to maintain engagement of the switch and electrode members 25, 26, and keep the switch S from reopening, because its closure no longer results in its thermostat 26 having opportunity to cool off as when a glow discharge that has closed the thermostat is shorted out; in other words, the starter S locks in. Ourrent thus flows continuously in the circuit H, without any possibility of interruption by the usual glow switch action of the starter S, and the lamp L ceases to flash. While the cathodes l i, ll are now heated continuously, this requires very little energy, and their steady subdued glow is not objectionable like the intermittent flashing or blinking of the lamp L as described above. Once established, the locked-in condition of the starter S continues as long as current flows in the circuit H.

However, if the circuit H is de-energized (by opening the hand switch l5, or by removing the defective lamp L and replacing it with a good one), and is allowedto remain de-energized long enough for the heater 3!] and the thermostat 26 to cool off fully, the starter S will open the circuitllandwillasainbereadyto'startthelamb in the usual manner.

For the convenience of those wishing to usemy & cent lamp are here given:

The lead-wires 22', 23 and 32, 33 may be of 25 mil nickel-wire. The thermostatic strip member 28 may be formed or the bimetal commercially known as Chace #2400 bimetal," composed of laminae of invar, an alloy of 64 per cent iron and 36 percent nickel, and of chrome iron, an alloy of 75 per cent iron, 22 per cent nickel, and 3 per cent chromium, in equal thicknesses, welded'together and coated with zinc on both sides; This strip 28 may be 0.008 inch thick; inch wide, and inch long. and may be bent intoa U with a bend oi slightly more than 180 having aradius o! 56 inch. The normal gap between member and contact 2! at ordinary atmospheric or room temperature may be 0.022 inch. H'Ihe heater may be a helical coil of about 1% inch (straight length) of nichrome wire of 0.0063 inch diameter wound on a 0.040 mil mandrel to the extent of 8 turns at turns per inch, giving a resistance 011.8 ohms, and its surrounding sleeve may consist of a 5 mm. length 5 01' #19 gauge none: glass tubing. having an external diameter of 0.140 mil and an internal .diametehof 0.060 mil. The nichrome' here referred to is an alloy of per cent nickel, 12 per cent iron, 11 per cent chromium, and 2 per cent What I claimas new and desire to secure by letters-Patent 0! the United States is:

l. The combination with a thermostatic glow switch comprising co-operating switch and electrode members one of which has a flexible thermostatic loop arranged to flex into engagement with the other member when heated by electric discharge between the members, thereby termihating said discharge, and to flex out o! engagement with said other member, when it cools. thereby restoring discharge between said members, of a resistance heater in said thermostatic loop connected in series with said glow switch and of capacity to heat said thermostatic loop to a temperature at which it maintains engagement with said other. member, and heat-shielding means around said resistance heater for delaying the heating of said thermostatic loop to engagement-maintaining temperature until after repeated closing and opening of the switch under the action of the glow discharge as above .set forth.

2. A thermostatic glow switch comprising a sealed envelope containing an io'nizable medium and cooperating spaced switch and electrode members arranged to sustain a glow discharge therebetween, one of said members being av bimetallic strip deformable by the heat of the said glow discharge to engage the other member and quench the discharge whereby said members alternately engage and disengage each other, and a resistance heater connected in series with said members and mounted to heat said bimetallic strip member, the thermal capacity of said heat er-being suflicient to delayeflective heating of said bimetallic strip member by the heater until said strip member has been deformed by the glow discharge into engagement with the cooperating member a predetermined numberv of times, the rate or heat transmission from the heater to the bimetallic strip member being greater than the rate of heat dissipation from said strip member. thereby holding said strip member in closed circuit position so long as cur- "won n. ma. 

